Progressive multifocal leukoencephalopathy (PML) is a fatal demyelinating disease of the central nervous system which results from reactivation of the latent polyomavirus JC virus (JCV) and its productive replication in glial cells of the human brain (Berger, J. R. (1995) J. Neurovirol. 1:5-18). Once a rare disease primarily seen in patients with impaired immune systems due to lymphoproliferative and myeloproliferative disorders, PML has become one of the major neurologic problems among patients with AIDS (Cinque, P., (2003). J. Neurovirol. 9(Suppl. 1):88-92).
It has been reported that between 4 and 8% of AIDS patients exhibit signs of PML, and JCV has been detected in the cerebrospinal fluid of affected patients, suggesting that there is active replication of the virus in the brain (Berger, J. R. (1995) J. Neurovirol. 1:5-18, Clifford, D. B., (2001) J. Neurovirol. 4:279). In addition, PML has recently been seen in patients undergoing experimental treatment with Tsybari, an anti VLA4 antibody, in combination with interferon. The histological hallmarks of PML include multifocal demyelinated lesions with enlarged eosinophilic nuclei in oligodendrocytes and enlarged bizarre astrocytes with lobulated hyperchromatic nuclei within white matter tracts of the brain (Cinque, P., (2003). J. Neurovirol. 9(Suppl. 1):88-92), although in some instances atypical features that include a unifocal pattern of demyelination and involvement of the gray matter have been reported (Sweeney, B. J., (1994). J. Neurol. Neurosurg. Psychiatry 57:994-997). Earlier observations from in vitro cell culture studies and an in vivo evaluation of JCV in clinical samples led to early assumptions that oligodendrocytes and astrocytes are the only cells which support productive viral infections (Gordon, J. (1998) Int. J. Mol. Med. 1:647-655). Accordingly, molecular studies have provided evidence for cell-type-specific transcription of the viral early genome in cells derived from the central nervous system (Raj, G. V., (1995) Virology 10:283-291). However, subsequent studies have shown low, but detectable, levels of JCV gene expression in normeural cells, including B cells, and noticeably high levels of production of the viral early protein in several neural and normeural tumor cells in humans (Gordon, J. (1998) Int. J. Mol. Med. 1:647-655, Khalili, K., 2003. Oncogene 22:5181-5191).
Like the other polyomaviruses, JCV is a small DNA virus whose genome can be divided into three regions that encompass the transcription control region; the genes responsible for the expression of the viral early protein, T antigen; and the genes encoding the viral late proteins, VP1, VP2, and VP3. In addition, the late genome is also responsible for production of an auxiliary viral protein, agnoprotein. T-antigen expression is pivotal for initiation of the viral lytic cycle, as this protein stimulates transcription of the late genes and induces the process of viral DNA replication. Recent studies have ascribed an important role for agnoprotein in the transcription and replication of JCV, as inhibition of its production significantly reduced viral gene expression and replication (M. Safak et al., unpublished observations). Furthermore, the agnoprotein dysregulates the cell cycle by altering the expression of several cyclins and their associated kinases (Darbinyan, A., (2002) Oncogene 21:5574-5581).
Thus far, there are no effective therapies for the suppression of JCV replication and the treatment of PML. Cytosine arabinoside (AraC) has been tested for the treatment of PML patients, and the outcome in some instances revealed a remission of JCV-associated demyelination (Aksamit, A. (2001) J. Neurovirol. 7:386-390). Reports from the AIDS Clinical Trial Group Organized Trial 243, however, have suggested that there is no difference in the survival of human immunodeficiency virus type 1 (HIV-1)-infected patients with PML and that of the control population, although in other reports it has been suggested that the failure of AraC in the AIDS Clinical Trial Group trial may have been due to insufficient delivery of the AraC via the intravenous and intrathecal routes (Levy, R. M., (2001) J. Neurovirol. 7:382-385). Based on in vitro studies showing the ability of inhibitors of topoisomerase to suppress JCV DNA replication, the topoisomerase inhibitor topotecan was used for the treatment of AIDS-PML patients, and the results suggested that topotecan treatment may be associated with a decreased lesion size and prolonged survival (Royal, W., III, (2003) J. Neurovirol. 9:411-419).
Double-stranded RNA molecules (dsRNA) have been shown to block gene expression in a highly conserved regulatory mechanism known as RNA interference (RNAi). WO 99/32619 (Fire et al.) discloses the use of a dsRNA of at least 25 nucleotides in length to inhibit the expression of genes in C. elegans. dsRNA has also been shown to degrade target RNA in other organisms, including plants (see, e.g., WO 99/53050, Waterhouse et al.; and WO 99/61631, Heifetz et al.), Drosophila (see, e.g., Yang, D., et al., Curr. Biol. (2000) 10:1191-1200), and mammals (see WO 00/44895, Limmer; and DE 101 00 586.5, Kreutzer et al.). This natural mechanism has now become the focus for the development of a new class of pharmaceutical agents for treating disorders that are caused by the aberrant or unwanted regulation of a gene.
Recent reports have indicated that in vitro, RNAi may show some promise in reducing JC virus replication (Radhakrishnan, S. (2004) J. Vir. 78:7264-7269, Orba, Y. (2004) J. Vir. 78:7270-7273). However, the RNAi agents examined were not designed against all know JC Virus strains and were not selected for stability and other properties need for in vivo therapeutic RNAi agents. Accordingly, despite significant advances in the field of RNAi, there remains a need for an agent that can selectively and efficiently silence a gene in the JC virus using the cell's own RNAi machinery that has both high biological activity and in vivo stability, and that can effectively inhibit replication of the JC virus for use in treating pathological processes mediated by JC virus infection.